The present application relates to an apparatus for determining the relative position of the plane of maximum amplitude of the spatial frequency in the optical image of an object, at least one grating being placed as a correlator and a spatial frequency filter after the entry objective, this grating located in the vicinity of an image plane of the objective and being further provided with a receiver system located behind the grating in the direction of the light flux. The output signals from the receiver system are used for controlling a display and/or adjusting instrument.
The state of the art of optical range finding systems incorporating an apparatus for determining the relative position of the plane of maximum amplitude of the spatial frequency in the optical image of an object may be ascertained by reference to U.S. Pat. No. 3,781,110 of Leitz, Heitmann and Schneider which issued Dec. 25, 1973. The disclosure of U.S. Pat. No. 3,781,110 is incorporated herein to further show the fundamentals relating to the use of push-pull signals as in the present invention.
Suggestions have been made in the prior art regarding such an apparatus to the effect that the prismatic adjusting or focusing screen of the viewing equipment be used as the spatial frequency filter in a single lens reflex camera.